Hand-held communication devices, particularly mobile telephones, personal digital assistants (PDA's), and the like, include a class of portable electronic devices, whose size enables them to be held in one hand while being operated with the other. Typical hand-held communication devices include a joystick for allowing a user to make selections while operating a hand-held device.
Many mobile phones on the market use a stepwise joystick which enables a user to move a cursor on the display only in a series of discrete steps, in four directions (e.g., left, right, up, and down), with the user clicking vertically on the stepwise joystick in order to select a desired item on the display.
Various analog joystick designs based on the optical reflection principle have been proposed. Such optical-reflection analog (ORA) joysticks may overcome the limitations of stepwise joysticks and the ORA joysticks may be used in mobile phones for applications, such as, for example, navigation, mobile gaming, and web browsing. ORA joysticks may enable movement over the full display screen in all directions (i.e., full 360° of direction), while also enabling the user to move the cursor with a continuous, variable speed, which is desired for navigation, web browsing applications, movement over a map, reading point-of-interest information, press-to-select, drag-and-drop, zoom, and similar mobile applications that use a user-controlled cursor, and are suited for use in a handheld device. Further details about analog joysticks are described in WO2010/035170, WO2010/020906, WO2009/125360 assigned to the present assignee, the entire contents of which are incorporated herein by reference.
In prior proposed approaches, enhanced performance could have only been achieved if all the applicable optical components, such as the light source, reflector or reflective element (e.g., reflector), and photodetectors of the joystick device were all well-aligned. Misalignment of any one of the optical components of the joystick device leads to asymmetry, degrading the performance of the device. Other approaches to overcome the misalignment problem have been proposed, but have also been observed to be costly and slow, especially for high-volume production.
FIG. 1 is a high-level schematic of a conventional optical joystick 100. The joystick 100 includes an IC package 111 having a substrate 102 on which lies, for example, an ASIC die 104, a light source 106 (e.g., LED), and a plurality of photodetectors 108 (e.g., photodiodes). A hard frame 110 supports a knob 116, which is hung directly above the light source 106. The knob 116 is hung on a suspension construction which includes a metal spring 112. A reflector 114 (that may be, for example, a mirror) is formed on the bottom side of the knob 116, directly facing the light source 106 such that light from the light source 106 is reflected by the reflector 114, towards photodetectors 108. The reflector 114 may be symmetrically-shaped (e.g., square or round shape). The light source 106 is located at a center of the photodiodes or photodetector configuration 108, with the photodetectors 108 located symmetrically around the light source 106, the details of which are illustrated in FIGS. 2A and 2B. The IC package 111 has a cavity 113 above the light source 106 and the photodetectors 108. It will be understood that the substrate 102 can be molded inside a transparent material which may also serve as an IC package while still permitting light to pass through the package. Further details of the joystick 100 have been described WO2010/035170, the entire contents of which are incorporated herein by reference.
Continuing to refer to FIG. 1, knob 116 is mounted on a suspension construction that allows the knob 116 to tilt around a rotation point when a force from a user's finger is applied, and is urged by the metal spring 112 to return to a central position (e.g., rest position) when the force is removed.
FIGS. 2A and 2B are side-views of the optical joystick of FIG. 1, with FIG. 2A depicting the knob in a rest position and FIG. 2B depicting the knob in a tilt position, respectively. FIGS. 2C and 2D are top-views of the optical joystick of FIG. 1, with the knob in a rest position in FIG. 2C and a tilt position in FIG. 2D, respectively. In FIGS. 2A-2D, all the applicable optical components may be in perfect alignment.
In operation, when the joystick 100 is in a rest position where no force from a user's finger is applied, the reflector 114 is positioned as perfectly parallel and centered to the plurality of photodetectors 108 and light source 106 as shown in FIG. 2A. In this position, a light spot reflected by the reflector 114 falls symmetrically on the photodetectors 108, thereby providing zero differential signals in the XY planes at differential circuits 201, quantified as Sx=Sy=0, as shown in FIG. 2C. When the joystick 200 is used by the user, such as for moving a cursor position on a display, the user, upon applying a force on the knob 116, causes the knob 116 to tilt, thus causing the reflector 114 to tilt proportionally in a direction, thereby resulting in non-zero differential signals in the X-axis and/or Y-axis at differential circuits 201 between the photodetectors 108 as shown as Sx≠0 in FIG. 2D. The differential signals Sx and Sy at the output of differential amplifiers in differential circuits 201 are converted into cursor speed in a desired direction. The differential signals Sx and Sy are proportional to the tilt angle of the reflector 114; therefore, a larger reflector tilt angle results in larger differential signals Sx and Sy, a faster movement of the cursor in a given direction.
Continuing to FIGS. 2A-2D, to select an item on the display, a user can use a click-to-select function of the joystick 200. In order to achieve this function, a user may have to move the cursor using the joystick 200 to a position of the item desired to be selected by the user, then stop the joystick 200 by releasing the knob 116, and then press down vertically with a certain force (i.e., clicking down on the knob 116). During the click action by the user, the reflector 114 moves horizontally downward. In this process, the differential signals on the photodetectors 108 remain substantially zero, but signal amplitude on the photodetectors 108 increases due to an increase in light irradiance falling on the substrate 102. By detecting a threshold in the common mode signal of all the photodetectors 108, the selection signal can be generated. In FIGS. 1 and 2A-2D, a relatively limited number of photodetectors are shown. It will, however, be understood that more or less photodetectors may be used as desired.
FIG. 3 shows a diagram illustrating a calculated differential signal as a function of the reflector angle, wherein a tilt angle of the reflector is shown on the X-axis and the differential signal is shown on the Y-axis. Specifically, FIG. 3 shows the differential signal (e.g., for X-Y detection) as a function of tilt angle of reflector 114 (FIG. 2A-2B) in the case of perfect alignment (e.g., the diagram with round datapoints shown as signal curve 1 301 in FIG. 3)—indicating it is symmetric with respect to a rest position (e.g., tilt angle=0) of the knob 116.
However, in the presence of misalignment, when the reflector 114 is displaced by a certain distance (e.g., 40 μm) from the rest position, the differential signal Sx, Sy becomes asymmetric, as illustrated in FIG. 3 as shown by signal curve 2 302. In this case, in the rest position, the differential signal is non-zero and the amount of signal change when the reflector 114 tilts with the same tilt angle in positive and negative directions is not symmetric anymore—this asymmetry causes degradation in the performance of the joystick 100. Albeit to a lesser extent, misalignment of the light source 106, and the initial angle of the reflector 114 at a rest position, as indicated in FIGS. 2B and 2D, may also contribute to the asymmetry of the differential signal, and thus degradation of performance of the joystick 100. Various correction schemes have been proposed without much success to correct large misalignment errors along with the slow times and high costs.